1. Technical Field of the Invention
The present invention relates to a dial operation device having a structure for informing an operator of a rotational position of a knob dial when a plurality of display sections provided in the knob dial are selectively illuminated.
2. Technical Background
FIG. 7 is a view showing a conventional structure of the above dial operation device. In this structure, a knob base 2 is fixed onto a printed circuit board 1. A knob dial 3 is attached onto an outer circumferential surface of this knob base 2. This knob dial 3 is provided with a plurality of linear light paths 3a. In the knob dial 3, there are provided a plurality of display sections 4 arranged at one end portion of each light path 3a, and these display sections 4 transmit light.
On the printed wiring board 1, there are provided a plurality of light sources 5 which are located on a rotational locus of the display section 4. When the knob dial 3 is rotated for operation along an outer circumferential surface of the knob base 2, electricity is supplied to a predetermined light source 5 according to a rotational position of the knob dial 3, so that light can be supplied to a predetermined display section 4 via a predetermined light path 3a. Then, the predetermined display section 4 is illuminated. When a plurality of marks 2a on the knob base 2 are selectively indicated, a rotational condition of the knob dial 3 is conveyed to an operator.
However, the following problems may be encountered in the above conventional structure. When the knob dial 3 is set at an intermediate position at which the display section 4 and the light source 5 are not opposed to each other, a beam of projection light sent from the light source 5 is intercepted by the knob dial 3. Therefore, no light is supplied to the display section 4. Therefore, light can not be supplied to the display sections 4 in the middle of rotation of the knob dial 3.